1. Technical Field
The disclosure concerns a plasma reactor for processing a workpiece such as a semiconductor wafer.
2. Background Discussion
The control of plasma processing uniformity in semiconductor fabrication is directly related to the performance of the fabrication equipment, such as a plasma reactor chamber. Recent developments in the semiconductor fabrication industry have imposed increased requirements on plasma processing uniformity control. For example, workpiece (wafer) size will increase from 300 mm to 450 mm in the foreseeable future, so that the wafer area that needs to be controlled is doubled. Also, plasma processing equipment tends to rely upon higher RF frequencies for better control of the radical and ion densities and, in some cases, to decouple the control of plasma ion and radical densities from the control of ion energies at the wafer surface. As both wafer size and excitation frequency increase, finite wavelength effects such as skin effect and standing wave effect severely affect the processing uniformity. There is also an electrostatic edge effect near the edge of the wafer which tends to increase or decrease the local processing rate. There are very few ways of electrically controlling plasma distribution or uniformity. Plasma distribution typically must be controlled by changing chamber parameters of the plasma reactor chamber, such as the ceiling-to-wafer gap, chamber pressure, gas flow rate and species of process gases, RF power level, or temperature. However, changes in such chamber parameters can negatively impact process results, or deviate from a desired process recipe while having only a limited impact upon plasma distribution or uniformity.
What is needed is a way of a strongly impacting plasma distribution without having to change chamber parameters, such as ceiling-to-wafer gap, chamber pressure, gas flow rate and species of feed stock gases, power or temperature, nor require the deviation of chamber parameters from values specified for them in a desired process recipe.